Is there a downside, like all programs yes. You have to manually make backups this is not done automatically when you edit a gpo. 

Let's start with the installation. Before you begin the installation of the software you have to make sure you have Group Policy Management Console installed on the server or workstation you want to install Backup Manager for Group policy.

After you downloaded the trail and installed the program it's time to start the program. The first thing you will have to do is select a Forrest to manage. In trailmode you may administer 3 gpo's. This is enough to see what the program can do. We have 3 gpo's and the one we want to backup is the Article gpo. As you can see at Figure 1 the top level is GPExpert Backup Manager for Group Policy. Then comes your domain and this is start looking familiar like your AD infrastructure. 

Figure 1

After you have chosen to backup the GPO the version number goes from 0 to 1. When you make another backup the fun starts, the version numbers goes up a few thousand. So reliable I don't know but you can easily select the date you made the backup and restore it.

At the GPO backups you can select easily a gpo to restore and your back to the settings that worked before you made changes that messed the settings up.

This program is still growing in strength but already very useful. They are developing more features into this tool like comparing backup's to current gpo which isn't possible yet but maybe a feature in the future? let's hope so.

Want to test it your self? go to SDM Software